In recent years, mobile phones, personal computers (PCs), PDAs (personal digital assistants), and other mobile electronic systems have significantly progressed in terms of multi-functionality and are typically provided with a lens module that provides them with imaging capability. In a mobile electronic system of this type, it is necessary to move a lens toward a subject or move the lens away therefrom along the optical axis so as to provide a camera module with autofocus capability.
A lens in a lens module has been typically moved by using a voice coil motor, a stepper motor, or any other driver in related art. In recent years, however, a driver using a polymer actuator device has been developed from the viewpoint of compactness. A polymer actuator device is formed, for example, of an ion exchange resin film sandwiched by a pair of electrodes, and the ion exchange resin film is displaced in the direction perpendicular to the film plane when a potential difference is produced between the pair of electrodes.
An example of a lens module using a polymer actuator device of this type has, for example, a configuration in which a movable lens frame that holds a group of lenses is supported by a guide shaft movably along the optical axis and a polymer actuator device is so positioned that it is aligned with the movable lens frame along the optical axis. According to the configuration described above, the movable lens frame is moved along the optical axis when the polymer actuator device is deformed (see JP-A-2006-293006, for example).
In another configuration of a lens module of this type, a set of polymer actuator devices that curve in directions different from each other are combined with each other, and a lens is disposed at one end of the polymer actuator device assembly (see JP-A-2006-172635, for example).